In recent years, means for rapidly transmitting information at the terabyte level have undergone marked development. It has become possible to transmit data and images comprising huge amounts of information. With this improvement in data transmission technology has come demand for recording and reproduction devices and recording media for recording, reproducing, and storing information with greater recording capacity.
Recording tapes are employed in a variety of applications, including audio tapes, video tapes, and computer tapes. Particularly, in the field of data backup tapes, as the capacity of the hard disks being backed up has risen, backup tapes with a recording capacity of several tens to 800 GB per reel have been commercialized. Further, high-capacity backup tapes exceeding 1 TB have been proposed, and the achievement of high recording capacity in such tapes is essential.
In achieving high recording capacity, high recording density techniques such as the use of magnetic powder in the form of microparticles, the high density filling of coatings with such microparticles, the smoothing of coatings, and reduction of the thickness of the magnetic layer have been proposed as approaches from the aspect of magnetic tape manufacturing. For example, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 8-306032 (“Reference 1” hereinafter, which is expressly incorporated herein by reference in its entirety) proposes the incorporation of a phosphorus-containing organic compound into the lower layer to enhance dispersion of inorganic powder in the lower layer and ensure the surface properties of the magnetic layer. Further, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 11-25442 (“Reference 2” hereinafter, which is expressly incorporated herein by reference in its entirety) proposes that the spatial frequency strength be determined by the ratio of long wavelengths to short wavelengths as an indicator of the surface smoothness of the magnetic layer.
However, when the surface smoothness of the magnetic layer is increased, there is a risk that uneven winding will occur and running properties will deteriorate. Accordingly, to prevent winding unevenness and the deterioration of running properties, a backcoat layer comprising a granular substance such as carbon black is provided on the surface of the support on the opposite side from the magnetic layer (for example, see Japanese Unexamined Patent Publication (KOKAI) No. 2004-30870 (“Reference 3” hereinafter, which is expressly incorporated herein by reference in its entirety)).
The magnetic layer surface roughness Ra is widely employed as an indicator in evaluating the surface properties of the magnetic layer. By contrast, Reference 2 proposes that the spatial frequency strength be determined by the ratio of long wavelengths to short wavelengths. This takes note of the fact that Ra is an average value, and for a given Ra, differences in the waviness component can greatly affect characteristics.
However, in magnetic recording media having a backcoat layer, simply controlling the surface properties of the magnetic layer results in the transfer of protrusions present on the backcoat layer to the surface of the magnetic layer, forming microindentations and generating so-called “reverse transfer” when the magnetic recording medium is stored in roll form during the manufacturing process and when the magnetic tape is stored wound on a reel hub after preparing as a finished product. This reverse transfer is problematic in that it compromises electromagnetic characteristics, particularly the BB-SNR and K-SNR (proximate noise). Since reverse transfer becomes pronounced following storage for extended periods and storage at elevated temperatures, magnetic recording media having backcoat layers present a problem in the form of roughness due to reverse transfer following storage, even when the initial surface properties of the magnetic layer have been controlled.